Homework 2
Assembly Language

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HW2 project

Overview

Understanding how different data types are defined appropriate operations is critical to developing correct software systems. Two's complement and unsigned representations are commonly used for numeric representations while ASCII is the most common representation for characters. To understand the operation of the machine it is first necessary to understand the theory and practice on which that operation is based, exercises will provide practice in numeric representations and operations.

Program development using assembly language demands the use of a run-time debugger that allows step-by-step program execution.

There are 2 parts to the homework.

Part 1

The following gives the homework program and the assembler listing of the program.

The program defines data and a few instructions that access the data.

INCLUDE Irvine32.inc

.data
; ----------------- Byte Values ---------------------
byte1		BYTE  'A'
byte2		SBYTE  -128

byteArray   BYTE  'A', 32, 41h, 00100010b

helloWorld BYTE "Hello World",0

; ----------------- Word Values ---------------------

word1		WORD   65535		; largest unsigned value
word2		SWORD  -32768		; smallest signed value
wordArray	WORD   1,2,3,4,5	; array of words

; --------------- DoubleWord Values --------------

dword1		DWORD   12345678h
dword2		SDWORD  -2147483648
dWordArray	DWORD	11111111h, 22222222h, 33333333h

; ------- QuadWord and TenByte Values ------------

quadWord1  DQ  234567812345678h
tenByte1   DT  1000000000123456789Ah

;------------------ Reals --------------------

real1  REAL4   -1.2
real2  REAL8   3.2E-260
real3  REAL10  4.6E4096

; The following ranges were discovered by trial and error:

ShortRealMax REAL4 9.9E+37		; maximum exponent
ShortRealMin REAL4 9.9E-38		; minimum exponent

LongRealMax REAL8 9.0E+307		; maximum exponent
LongRealMin REAL8 9.9E-308		; minimum exponent

ExtRealMax REAL10 9.9E+4931		; maximum exponent
ExtRealMin REAL10 9.9E-5199		; minimum exponent

; ----------------- Pointers ---------------------

ptrByteArray    DWORD  byteArray	; points to byteArray
ptrWordArray    DWORD  wordArray	; points to wordArray

.code
main PROC
	mov		al, byte1
	mov		ah, helloWorld[ 6 ]
	mov		bx, word1
	mov		cx, wordArray[ 3 ]
	mov		eDx, dword1
	mov		eSi, dWordArray[ 2 ]
	exit
main ENDP
END main

 00000000			.data
				; ----------------- Byte Values ---------------------
 00000000 41			byte1		BYTE  'A'
 00000001 80			byte2		SBYTE  -128

 00000002 41 20 41 22		byteArray   BYTE  'A', 32, 41h, 00100010b

 00000006 48 65 6C 6C 6F	helloWorld BYTE "Hello World",0
	   20 57 6F 72 6C
	   64 00

				; ----------------- Word Values ---------------------

 00000012 FFFF			word1		WORD   65535		; largest unsigned value
 00000014 8000			word2		SWORD  -32768		; smallest signed value
 00000016 0001 0002 0003	wordArray	WORD   1,2,3,4,5	; array of words
	   0004 0005

				; --------------- DoubleWord Values --------------

 00000020 12345678		dword1		DWORD   12345678h
 00000024 80000000		dword2		SDWORD  -2147483648
 00000028 11111111		dWordArray	DWORD	11111111h, 22222222h, 33333333h
	   22222222
	   33333333

				; ------- QuadWord and TenByte Values ------------

 00000034			quadWord1  DQ  234567812345678h
	   0234567812345678
 0000003C			tenByte1   DT  1000000000123456789Ah
	   1000000000123456789A

				;------------------ Reals --------------------

 00000046 BF99999A		real1  REAL4   -1.2
 0000004A			real2  REAL8   3.2E-260
	   0A0F7D228322BAF5
 00000052			real3  REAL10  4.6E4096
	   7527E1D52B1C853F14BF

				; The following ranges were discovered by trial and error:

 0000005C 7E94F56A		ShortRealMax REAL4 9.9E+37		; maximum exponent
 00000060 0206C077		ShortRealMin REAL4 9.9E-38		; minimum exponent

 00000064			LongRealMax REAL8 9.0E+307		; maximum exponent
	   7FE005419221015D
 0000006C			LongRealMin REAL8 9.9E-308		; minimum exponent
	   0031CC12CFA686A2

 00000074			ExtRealMax REAL10 9.9E+4931		; maximum exponent
	   7FFED505D9D5BF6936E4
 0000007E			ExtRealMin REAL10 9.9E-5199		; minimum exponent
	   00000000000000000000

				; ----------------- Pointers ---------------------

 00000088 00000002 R		ptrByteArray    DWORD  byteArray	; points to byteArray
 0000008C 00000016 R		ptrWordArray    DWORD  wordArray	; points to wordArray

 00000000			.code
 00000000			main PROC
 00000000  A0 00000000 R		mov		al, byte1
 00000005  8A 25 0000000C R		mov		ah, helloWorld[ 6 ]
 0000000B  66| 8B 1D			mov		bx, word1
	   00000012 R
 00000012  66| 8B 0D			mov		cx, wordArray[ 3 ]
	   00000019 R
 00000019  8B 15 00000020 R		mov		eDx, dword1
 0000001F  8B 35 0000002A R		mov		eSi, dWordArray[ 2 ]
					exit
 0000002C			main ENDP

				END main

The debugger can be used to examine memory as the program executes.

For example, from the listing above, we can locate the variable offset (0x00000020) in memory, then find its value at the address (0x00404020) in memory:

00000020 12345678 dword1 DWORD   12345678h

dword1 variable is at address 00404020 and contains 12345678h.

0x00404000 41 80 41 20 41 22 48 65 6c 6c 6f 20 57 6f 72 6c A€A A"Hello Worl 0x00404010 64 00 ff ff 00 80 01 00 02 00 03 00 04 00 05 00 d.ÿÿ.€.......... 0x00404020 78 56 34 12 00 00 00 80 11 11 11 11 22 22 22 22 xV4....€...."""" 0x00404030 33 33 33 33 78 56 34 12 78 56 34 02 9a 78 56 34 3333xV4.xV4.šxV4 0x00404040 12 00 00 00 00 10 9a 99 99 bf f5 ba 22 83 22 7d ......š™™¿õº"ƒ"} 0x00404050 0f 0a bf 14 3f 85 1c 2b d5 e1 27 75 6a f5 94 7e ..¿.?..+Õá'ujõ”~ 0x00404060 77 c0 06 02 5d 01 21 92 41 05 e0 7f a2 86 a6 cf wÀ..].!’A.à.¢.¦Ï 0x00404070 12 cc 31 00 e4 36 69 bf d5 d9 05 d5 fe 7f 00 00 .Ì1.ä6i¿ÕÙ.Õþ... 0x00404080 00 00 00 00 00 00 00 00 02 40 40 00 16 40 40 00 .........@@..@@.

Variables and registers can also be viewed individually in a watch window.

Turn in

Circle and label the following variables in the memory listing below:

1. byte1
2. helloWorld[ 6 ]
3. word1
4. wordArray[ 3 ]
5. dword1
6. dWordArray[ 2 ]

0x00404000 41 80 41 20 41 22 48 65 6c 6c 6f 20 57 6f 72 6c A€A A"Hello Worl 0x00404010 64 00 ff ff 00 80 01 00 02 00 03 00 04 00 05 00 d.ÿÿ.€.......... 0x00404020 78 56 34 12 00 00 00 80 11 11 11 11 22 22 22 22 xV4....€...."""" 0x00404030 33 33 33 33 78 56 34 12 78 56 34 02 9a 78 56 34 3333xV4.xV4.šxV4 0x00404040 12 00 00 00 00 10 9a 99 99 bf f5 ba 22 83 22 7d ......š™™¿õº"ƒ"} 0x00404050 0f 0a bf 14 3f 85 1c 2b d5 e1 27 75 6a f5 94 7e ..¿.?..+Õá'ujõ”~ 0x00404060 77 c0 06 02 5d 01 21 92 41 05 e0 7f a2 86 a6 cf wÀ..].!’A.à.¢.¦Ï 0x00404070 12 cc 31 00 e4 36 69 bf d5 d9 05 d5 fe 7f 00 00 .Ì1.ä6i¿ÕÙ.Õþ... 0x00404080 00 00 00 00 00 00 00 00 02 40 40 00 16 40 40 00 .........@@..@@.

Part 2

The algorithm (code) of the HW2 program moves data from variables to registers.

The execution can be followed using the debugger.

Program algorithm

.code main PROC mov al, byte1 mov ah, helloWorld[ 6 ] mov bx, word1 mov cx, wordArray[ 3 ] mov eDx, dword1 mov eSi, dWordArray[ 2 ] exit main ENDP

Assignment

1. Download HW2 project.
2. Open Project.sln, Visual Studio should open the project.
3. From the menu select: Debug | Start Debugging
4. The debugger should pause at a breakpoint and display the register window at instruction:

   mov al, byte1

   

5. Clicking F11 key will execute the next instruction.

Turn in

Use the debugger to execute each instruction of the program algorithm.

List the variable offset, register effected, and resulting register values for each instruction executed.

For example, for the instruction and offset of variable helloWorld in the above listing:

Instruction	Offset	Register	Value
mov cl, helloWorld[ 4 ]	0000000A	cl	6F or 'o'

 00000006 48 65 6C 6C 6F helloWorld BYTE "Hello World",0
   20 57 6F 72 6C
   64 00
 

Instruction	Offset	Register	Value
mov al, byte1
mov ah, helloWorld[ 6 ]
mov bx, word1
mov cx, wordArray[ 3 ]
mov eDx, dword1
mov eSi, dWordArray[ 2 ]